New Post: LayoutUpdateStrategy always provide null destinationContainer

I have implemented ILayoutUpdateStrategy but I can't get a valid destinationContainer in the "BeforeInsertAnchorable" method.

Then I wonder how can I setup the DockWidth or DockHeight property?
And I also don't understand why my LeftSide, RightSide ... are always in "auto hide" mode?

In the end I miss some documentation on this interface.
Thanks for any help.